Dallas police chief David Brown said in a briefing, Johnson was killed by a police-controlled robot bomb after a standoff with law authorities and the latter told the negotiators that he had no group affiliation.

Furthermore, negotiators also said that the suspect was upset to the various killings to black people by police authority.

The shooting comes in the center of national debates over racial disparities on criminal justice system and use by force of police.

US president Barack Obama condemned the attack and even called it as “vicious, calculated and despicable.” He also cut short his trip to NATO summit in Europe to visit Dallas.

The Dallas incident is considered as the worst police shooting in the American history.